I was given three pieces of advice for climbing Snowdon: set off in the wet, arrive in the dry; don't, on any account, take the Llanberis Path; and leave before 8am.

"Right, lads, it's 9.30. The sun's out. We're going up the Llanberis Path," said Tom, our team leader for the day, at the end of breakfast.

An hour later, we'd reached the open moorland above the Llyn Peris reservoir. The footpath ahead was thick with hikers of every shape, size, age and ethnicity. I wondered – just as visitors to this wild country in the corner of North Wales must have wondered frequently over the past 200 years – what the hell all these people were doing here.

The poet RS Thomas knew Snowdonia well. He wrote that folk come to these mountains "seeking for something unnameable, a lost Eden, a lost childhood: for fulfilment, for escape, for refuge, for conquest of themselves, for peace, for adventure. The list is endless. The hills have all this to give and more."

Today, half a million people stand proudly on the summit every year, the vast majority arriving between April and October. Snowdon is Britain's busiest mountain by some margin. It has been since the early 19th century, when the Napoleonic Wars imposed the "staycation" on a generation of adventurers who had recently discovered the Alps.

When the novelist George Borrow set off from Llanberis with his daughter and a guide in 1843, they were "far from being the only visitors to the hill this day; groups of people, or single individuals, might be seen going up or descending the path as far as the eye could reach".

At 3,560ft, Snowdon (Yr Wyddfa in Welsh, meaning "the throne") is the highest mountain in England and Wales. This is the key to its enduring popularity. (The second-highest is Carnedd Llewelyn, a mere 70ft lower, but who's heard of it, let alone climbed it?) There are seven main paths to the summit. The Llanberis Path, which roughly follows the route of the Snowdon Mountain Railway, is one of the longest, and certainly the easiest.

The author takes a break as he cycles down the Rangers Path. Photograph: Observer

We were a team of nine old acquaintances who had come to ascend Snowdon on mountain bikes, and fundraise for a mutual friend who is terminally ill. Changing the first of many punctures beside the path, I was able to watch the extraordinary digest of British society wearily climbing the mountain. There were others using the day as a means to raise money for charity: a band of pirates walked past; three men in 1950s tea dresses and long gloves smiled demurely and I stuffed my copper coins into a collecting tin carried by two girls who were picking their way up, three-legged. I half-hoped to encounter some lads dressed like the soldiers in Carry On Up the Khyber – it was, after all, filmed on Snowdon in 1968.

A father-and-son team illustrated the confusion at the heart of our nation's relationship with the outdoors: the dad had more kit than Doug Scott going off to climb K2, while his son was in jeans and a T-shirt that exclaimed, in pink, "I like party girls". I saw several couples whose expedition equipment comprised Tesco bags and a senior gentleman who was transporting the remains of the family picnic down the mountain in a red tartan shopper – a wonderful and uniquely British sight which I'll call upon in low moments for years to come.

Half an hour before we reached the top, we ascended into the curtain of mist. Some form of cloud, mist or fog seems to perpetually crown Snowdon. It shifts over the mountain's buttresses, curls round the cwms and folds into the grey gulleys, occasionally clearing to let iridescent light on to the broken pieces of rock that have been splintered by the freeze and thaw of endless bitter winters.

The first recorded ascent of Snowdon was in 1639. The botanist Thomas Johnson gained the summit and noted: "British Alps veiled in cloud." Welsh naturalist Thomas Pennant, who did much to popularise Snowdonia to painters, poets and the public alike in the late 18th century, also reached the top to find "a vast mist enveloped the whole circuit". German painter and physiologist Carl Gustav Carus made it up in 1844. "Of course, no sign of any view," he wrote.

I've climbed Snowdon twice before. My family came to North Wales on holiday in June 1974 when I was seven. We made sandcastles, played crazy golf and ate ice-creams, all in the rain. On the day the heavens demonstrated the full arsenal of Welsh precipitation, I followed my dad silently up Snowdon. At the top it had actually stopped raining, but cloud clung to mountain like wet cotton wool. Rounding the pyre of grey rocks at the summit, I was astonished to make out the shapes of a family enjoying a flask of coffee and biscuits. Then we set off down, still in silence. My second ascent was late on a Sunday afternoon in summer 20 years ago, at the end of a long weekend climbing the highest peaks in Scotland, England and Wales. Again, the cloud as dense as a London pea-soup fog in the 1950s.

The Snowdon railway for those who can't face the walk. Photograph: Alamy

The summit cafe, which opened for the 2011 summer season the day we went up, was heaving. The new award-winning building, Hafod Eryri, has gone some way to quelling centuries of public opprobrium at the hospitality offered on top of the mountain. George Borrow stopped for a beer on the summit, in what he called "a rude cabin". The Victorian hotel, built when the railway was completed in 1896, was replaced in 1935 with a visitor centre and restaurant designed by Clough Williams-Ellis, the architect behind Portmeirion. Towards the end of the 20th century this building was so down at heel that Prince Charles described it as the "highest slum in Wales". After an £8.5m makeover Hafod Eryri has finally satisfied centuries of protesters. It's just that we couldn't get inside it.

"Don't even attempt it," said Paulo, who was waiting to greet me at the top. "It's like the evacuation of the American embassy during the fall of Saigon in there. If they're not looting the place yet, it's imminent."

Minutes later, our day was transformed. The cloud was lifting. For the first time, we could see the pyramid-shaped peak. The barren slopes, the horseshoe ridges and the moorland below all left an impression of "grandeur and desolation", as William Wordsworth once wrote.

Having pushed our bikes much of the way up, we were glad to be riding them again. Descending the Rangers Path was technically difficult. We edged along the Clogwyn Du'r Arddu cliff face on a loose path that shifted every time we touched the brakes, and down through several hairpins to Llyn Ffynnon-y-gwas. There were more mechanical failures and several crashes, but the mountains were suddenly our own.

Some of the half million people who make it to the top of Snowdon each year. Photograph: Andrew Price / Rex Features

As with dialects, there are a hundred regional variations to the light in the British Isles. On the west coast of Scotland the Atlantic light has vitality that you don't find anywhere else. The soft landscapes give the light in East Anglia a thinned beauty, like young wine. There is menace in the cold light of Dartmoor. And in the mountains of North Wales, the light is distinctive again. When the sun finally broke through and filled the valley floor below us it was lustrous, heavily suspended with moisture, soothing and somehow suggestive of mythical happenings.

To the Welsh, Snowdonia is the heartland – the final refuge when the Romans and the Normans invaded. Owain Glyndwr, the last native Prince of Wales, reigned here. In the national anthem "Land of My Fathers", the Welsh sing of their love for the land, not for a sovereign. Looking west over lakes, forests and proud hills, I understood why. Like the song, Snowdonia is rich – in colour and variety of terrain – and rhythmic, in the way the sculpted mountain ridges, valleys and tarns are repeated. As for scale, you could fit the whole landscape into one Alpine valley.

We climbed again, over the Maesgwm pass, and dropped into a perfect, glacial-shaped valley. We had one long, lovely descent left, but we lingered on the hillside. Only when the light on Snowdon turned orange did we accept the day was done, and ride back down to Llanberis.

Essentials

• The following correction was printed in the Observer's For the record column, Sunday 8 May 2011. We said Snowdon's Welsh name of Yr Wyddfa meant "the throne". It actually means tumulus or burial mound. (It may refer to the cairn thrown over the mythical giant Rhitta Gawr after his defeat by King Arthur.)